1. Field of the Invention
The present invention relates to a frame rate conversion apparatus, a frame rate conversion method, and a computer-readable storage medium that convert the frame rate of an input image (input frame).
2. Description of the Related Art
Display apparatuses are roughly classified according to their display characteristics into either an impulse type or a hold type. An apparatus such as a liquid crystal panel which holds a display almost uniformly during one frame period as shown in FIG. 12B will be referred to as a hold-type display apparatus. In contrast, an apparatus with a short period of light emission in one frame as shown in FIG. 12A will be referred to as an impulse-type display apparatus.
Impulse-type display apparatuses include a CRT (Cathode Ray Tube) and a field-emission type display. In impulse-type display, pixels repeatedly blink, and hence the display has a characteristic that causes flicker. That is, the screen appears to flicker. A higher luminosity and larger area correspond to easier flicker detection. With the recent tendency toward larger display screens, flicker on impulse-type display apparatuses is increasingly becoming a problem to be solved.
Methods of reducing flicker include a method of displaying an image at a higher frame rate by distributing an input frame into a plurality of sub-frames at an arbitrary ratio. If, for example, the frame rate is doubled by distributing an input frame into two sub-frames at a ratio of 6:4, since the frequency of flickering increases, flicker becomes difficult to detect.
However, when a user views this display, as shown in FIG. 13, a pseudo-contour, which depends on a visual characteristic, occurs because a temporally succeeding sub-frame can be seen to shift from line-of-sight tracking during a given frame period.
In order to reduce a pseudo-contour, there is disclosed a method of reducing a pseudo-contour by increasing/decreasing a high frequency component of the spatial frequency of a sub-frame (Japanese Patent Laid-Open No. 2002-351382).
According to the technique disclosed in Japanese Patent Laid-Open No. 2002-351382, however, since only a high frequency component is controlled, tailing-blur may occur when an image moves. FIG. 14 shows the relationship between an outline of a display output when the technique disclosed in Japanese Patent Laid-Open No. 2002-351382 is used and the manner of how the display output is seen. Referring to FIG. 14, the luminance of a low-frequency component is left in a temporally succeeding sub-frame in one frame period. In this case, the luminance of this low-frequency component causes tailing-blur.